The present invention relates to an image-receiving sheet for thermal transfer printing such as an image-receiving sheet provided with a dye receptor layer capable of receiving sublimation dye transferring from a sublimation thermal transfer sheet, and particularly relates to a thermal transfer image-receiving sheet which can widely be utilized in a field of various kind of color printers such as a video printer.
In recent years, there has been remarkable progress in a photographing technology and systems for formation of images exemplified by computer graphics. Along with such progress, there has been a great demand for making colored hard copies of images.
Sublimation thermal transfer method is known as one of systems for making colored hard copies. According to the sublimation thermal transfer method, a thermal transfer sheet using sublimation dye as recording agent is placed on a thermal transfer image-receiving sheet, and then the sublimation dye is transferred to the thermal transfer image-receiving sheet by heating the thermal transfer sheet in correspondence with electric record signals for printing with the use of a heating means such as a thermal head, whereby images are printed.
Of many kinds of systems for making colored hard copies, public attention has been attracted by the sublimation thermal transfer method, because that method is excellent in such various properties of an obtained image as transparency, reproducibility of gradation in neutral tints and reproducibility of colors, and it is possible to realize a high quality image being equal to silver salt photograph.
There is also known as one of such a sublimation thermal transfer image-receiving sheet, that of a pressure sensitive adhesive sheet type. That type of sublimation thermal transfer image-receiving sheet is provided with a dye receptor layer having adhesiveness on its back surface and a release sheet such as a release paper temporarily bonded to the adhesive back surface of the receptor layer. The Dye receptor layer of such an image-receiving sheet is peeled off the release sheet after the formation of desired images, and then stuck to any object.
FIGS. 8, 9 and 10 show one example of prior art with respect to such a sublimation thermal transfer image-receiving sheet of the pressure sensitive adhesive sheet type, and FIG. 9 is an enlarged Y--Y sectional view of FIG. 8. As shown in FIG. 8, this sublimation thermal transfer image-receiving sheet is of a continuously long sheet having a certain width, which is subjected to a half-cut process to form a prescribed shape defined by cut lines (half-cut lines) 59. A reference numeral 62 in FIG. 8 indicates a detection mark.
As shown in FIG. 9, this sublimation thermal transfer image-receiving sheet is prepared by laminating, on a release surface of a release sheet 55, a layered product which is composed of an adhesive layer 54 adhering to the above-mentioned release surface, a support 52 made of sheet-like material such as a foamed polyethylene terephthalate (PET) film and a synthetic paper called "YUPO" (product name), and a dye receptor layer (i.e. a layer of resin having dyeing property) 53 formed on the support 52. The cut line (half-cut line) 59 stops at a depth corresponding to a thickness of the adhesive layer 54. Therefore, the release sheet 55 is not divided by the cut line (half-cut line) 59.
As shown in FIG. 8, such sublimation thermal transfer image-receiving sheet both ends of which are wound around cores 63 for wind respectively is mounted in a printer, and fed toward a direction indicated by an arrow or a direction opposite thereto. Then a sublimation thermal transfer sheet (not shown in FIG. 8) is placed on the sublimation thermal transfer image-receiving sheet. Thereafter, sublimation dye of the sublimation thermal transfer sheet is transferred to the surface of the sublimation thermal transfer image-receiving sheet by heating the sublimation thermal transfer sheet in correspondence with the image to be printed from its back surface side with the use of a heating means such as the thermal head to form a desired image 60 in an area defined on the sublimation thermal transfer image-receiving sheet by the cut line 59.
The area in which the image 60 (for example, a photograph of portrait) has been given is separated from a surrounding portion by the cut ine 59 as the border line, and peeled off the release sheet 55 together with the adhesive layer 54. Then, as shown in FIG. 10, the thus peeled portion A of the dye receptor layer in which the image 60 has been given is stuck to an object 65 such as a notebook, a pocketbook, a bag, and the like.
As mentioned above, in the conventional art, the foamed resin film or the synthetic paper is used as the support 52 of the thermal transfer image-receiving sheet so as to bear an impact force given from the thermal head, and so as to prevent diffusion of heat given from the thermal head.
However, because the area defined by the cut line 59 is comparatively narrow, when the minute or highly detailed image 60 in various colors is formed in such a narrow area, lowering of a density of the image is liable to be caused, particularly at a high density portion in the image such as a black portion colored by superimposition with colors of yellow, cyan and magenta, resulting in occurrence of a problem that the obtained image is weak in a visual impression, that is, lack of so called punch, and the image is blur. Under such circumstances, there has been required to realize a formation of a powerful image having so-called punch.
Besides, when the image is printed with the use of the conventional thermal transfer image-receiving sheet as shown in FIG. 8, the thermal transfer image-receiving sheet both ends of which are wound around the cores 63 respectively is fed through a platen roller and another roller in the printer for formation of the image, and thereafter, a portion of the thermal transfer image-receiving sheet, in which the image is to be given is locally heated by the thermal head and the like to form the desired image. During the printing process mentioned above, there may occur a phenomenon that an edge portion of the area defined by the cut line 59 is turned up through a bend of the thermal transfer image-receiving sheet when the thermal transfer image-receiving sheet passes through the roller portion or another portion, with the result that the area is peeled off. Furthermore, because the area to be peeled has the adhesive layer formed on its back surface, the peeled piece of the area may adhere to the thermal head or another portion in the printer. Accordingly, there has been caused a problem that a feeding or carrying obstruction of the thermal transfer image-receiving sheet occurs in the printer to interrupt the printing process.
The above problem may be solved by increasing an adhesive strength of the adhesive layer. However, when the adhesive strength of the adhesive layer is increased, there occurs a problem of difficulty in peeling of the half-cut area after formation of the image, and occurs another problem that a part of the area to be peeled is torn at the time of peeling.